For now use RArch's solution. This is caused by a missing change during the time when I took over primary development of the merge system from Ryan Gordon, and completely my fault. I totally missed adding the code to create this column. Basically he told me it was only in the trunk, not the branch, and I forgot.

I've attached a fixed functions.php, which will require restarting the whole merge (don't forget to restore your backup of MyBB from before you started merging), or you can manually add the column using RArch's comment, and the merge will automatically remove it with the fixed functions.php.

Thanks for finding and reporting bugs so quickly, and apologies for my malf-up.